WB jr. Q&A

[boB]

I added a Tinyurl for the latest and greatest beta code.  For the moment, it is this...

http://tinyurl.com/l5ua8ga

boB

[phonetic]

I find its not easy to get 50mV current shunts in AU, most  here are 75mV, can the wizbang support 75mV shunt voltage ??

[boB]

I find its not easy to get 50mV current shunts in AU, most  here are 75mV, can the wizbang support 75mV shunt voltage ??

Yes, I believe so.  There is a modbus register that ~should~ allow it to be adjusted to have lower
post processing gain.  The modbus document has not been updated yet but here is the modbus
register/address...

Register 4363 or Address 4362   is a number that is normally sitting at zero called   WbJrNumeratorSS

This is a 16 bit signed number  +- 32,767  that will raise the effective gain if you bring it up to
a maximum of 32,767 or reduce the gain if you make it negative, 32,769 up to 65,535.

I can't remember off hand how much the gain will vary.  It was mainly meant as a ~tweak" adjustment
but I ~think~ it may just make that 50 mV work at 75 mV without having to command a gain
change of the shunt amplifier from 8 down to 4 which would be 1/2 and by itself not very
useful to you.

I will calculate the adjustment range of that tweak number and post it.

boB

[phonetic]

Bob, many thanks, as always..your a legend.

[dgd]

I find its not easy to get 50mV current shunts in AU, most  here are 75mV, can the wizbang support 75mV shunt voltage ??

FYI, Jaycar carry a good range or 50mv shunts ranging from 1A to 200A, they don't seem to have 75mv shunts anymore.
If you want real 50mv Deltec types up to 500A then Ebay.au always seems to have them available and often from oz suppliers too.
Also if you don't mind paying too much then Element14 for Datel 50mv types, or RS also carry many 50mv shunts.

dgd

[mtdoc]

boB or others -  Any plans to publish the specs on this?  Resolution, accuracy, temp coefficient, etc... ?

Just wondering since I am building my own "back box" to more accurately measure shunt current and also AC current in my ePanel.  I'm just not satisfied with the FlexNet DC's resolution or accuracy.

Regardless, I'm sure I will end up buying one of these anyways since I am a monitoring junkie and will want to be able to control charging with this info.   

I guess I could just wait and see what ADC and voltage reference you're using.. I'm just impatient and curious.... It's  nice of you to use a nice clear plastic case but the pictures aren't quite high enough resolution to make out the components..

[boB]

The worst case accuracy I measured seemed  to be around +- 0.4 percent but was only a comparison of using a Fluke meter across the same shunt the WB Jr. was connected to.  (voltage across the sense screws) I have not pulled out the Yokagawa yet.

The resolution is 0.1 amps and is very good.  The Deltec shunts are spec'd at +- 0.25 percent.

I wish I had a golden standard for current to check against but we have some decent equipment here.
Haven't come up with a general specification.

The A/D  is self calibrating for offset in between each measurement.

I am pretty sure that you are not going to find a DC current measurement  better than this.

Shunts other than the Deltec as far as sense screw spacing will require some kind of
adapter which I hope we can make.

More hard specifications as we have time.

boB

[mtdoc]

Thanks for all the bits boB!

[RossW]

Shunts other than the Deltec as far as sense screw spacing will require some kind of
adapter which I hope we can make.

Next board revision, how about one hole and one slot?

[boB]

Shunts other than the Deltec as far as sense screw spacing will require some kind of
adapter which I hope we can make.

Next board revision, how about one hole and one slot?

Yeah, maybe but I wouldn't hold my breath.  There just isn't any room.

I also wouldn't hold my breathe on the bracket.  You will have to wire something up
for now to make non-standard shunts work.

So, we just tested an off the shelf Delta shunt along with one of our Yokogawa power meters and
the current matches within +- 0.1 amps  !   Mostly it is right on but that's about as far off
as we can see it going.  The resolution of the A/D converter is actually 0.078125 amps so
software has to scale and round, etc.

This is REAL good !

boB

[mtdoc]

So, we just tested an off the shelf Delta shunt along with one of our Yokogawa power meters and
the current matches within +- 0.1 amps  !   Mostly it is right on but that's about as far off
as we can see it going.  The resolution of the A/D converter is actually 0.078125 amps so
software has to scale and round, etc.

This is REAL good !

boB

Yes, that sounds great boB!  So 16 bit ADC and a 5.12 V reference?

[boB]

Yes, that sounds great boB!  So 16 bit ADC and a 5.12 V reference?

It certainly appears to calculate out to that, doesn't it ?   But no, it's 2V.

This thing should be good for plus and minus 2,500 amps with the 500A/50mV scaling.

High enough for large surges.

[Vic]

Has anyone found a retailer that knows when they will have them in stock?

Well there appears to be some miss information going on with the retailers and Midnite. I sent a note to NAWS and this is their reply.      <<<  ...

Noticed last night that at least Wind-Sun had a listing for the MNWBjr:
http://www.solar-electric.com/midnite-solar-whiz-bang-jr-current-sense-module.html

There is NO stock and NO Due Date,  but,  at least some progress.  FWIW.  Christmas in November??   Vic

[mtdoc]

Yes, that sounds great boB!  So 16 bit ADC and a 5.12 V reference?

It certainly appears to calculate out to that, doesn't it ?   But no, it's 2V.

This thing should be good for plus and minus 2,500 amps with the 500A/50mV scaling.

High enough for large surges.

+/- 2500 amps!!!!!   Yeah I'd say that oughta cover it........

And let's see at 96 max amps per Classic - that comes out to 26 Classics - I only have 23 to go before I'll outgrow it....

[Tons001]

Crap ... I paid $59 elsewhere. I should have waited two more days and paid $44 here.